The present invention relates to an impacting arrangement in general, and more particularly to pile drivers.
Pile-drivers of various constructions are already known and in widespread use. Usually, the include a housing which receives an impacting body, such as a ram, and allows it to move up and down, parallel to the longitudinal axis of the pile to be driven. A conventional pile-driver also may include a slidable impact-transmitting ram follower which is interposed between the free end of the pile to be driven and the ram.
A device of this type is disclosed in the German published patent application DT-OS No. 2,454,488.
In this device, a plurality of annular rubber elements is arranged between the housing and the ram follower around that surface of the follower which is struck by the ram. These annular rubber elements serve to protect the housing from the recoil forces which are reflected back from the ram follower to the housing immediately after the ram strikes the ram follower. Here, a relatively huge elastic value is necessary to absorbing recoil energy. Since all the elements must surround the surface of the follower which is struck by the ram, and must be spaced from each other, the housing must be enlarged to accommodate the elements and must have a considerably greater diameter than that of the pile to be driven. During operation of this device, this diameter difference subjects the housing to considerable bending stresses. Also, the enlarged housing prevents closely-spaced piles from being driven independently. In such instances, the protection against the recoil must be dispensed with altogether, or must be reduced to such an extent that the durability of the device is adversely affected.
In order to anchor offshore drilling platforms on the continental shelf or the like, tubular piles are now used which have a diameter of about 1 meter and a length of 100 meters or more. These piles require very high impacts in order to drive them into the bottom strata. The devices which are used for this purpose have large-diameter rams, to reduce the specific surface pressures by increasing surface area and thereby increasing their durability. Since the piles used in this application are considerably resiliently deformed on impact because of their large lengths, and since they thus transmit a high amount of energy to these devices during their recoil, it is necessary to protect the devices from damage caused by the recoil. Conventionally, this requires enlargement of the housing. Inasmuch as tubular piles which are being used in the offshore pile-driving operations are usually guided in pile guides which are fitted to the outer diameter of the tubular piles, an enlarged housing cannot drive a pile past the top of its guide, because the housing is too big to enter the guide.